Process of sweetening petroleum distillates



Jan. 4, 1944. M. c. K. JONES E-rAl. 2,338,585

PROCESS 0F SWEETENING PETROLEUM DISTILLATES Filed Oct. 29, 1941 Oll- 0UTL ET Patented Jan. 4, 1944 PROCESS F SWEETENING PETROLEUM DISTILLATESMinor C. K. Jones, Bound Brook, and Richard C.

Brandon, Elizabeth, N. J., assignors to Standard Oil DevelopmentCompany, a corporation of Delaware Application Octoberv 29, 1941, SerialNo. 416,963

9 Claims.

This invention relates to the art of sweetening petroleum distillatesinvolving the dispersion oi a metal sulfide, e. g., lead sulfide, in thesweetened petroleum distillate, and has the object of facilitating theseparation and recovery of the metal sulfide from ,the sweeteneddistillate.

Sweetening treatments are used to improve odor, correct corrosion, andeliminate sulfurcontaining compounds which have deleterious effects onthe stability and combustion qualities of hydrocarbon oils. Mercaptansare the sulfurcontaining impurities which are largely responsible forthe need of sweetening petroleum distillates, and in a number ofsweetening treatments, they are reacted with salts of metals, such aslead, copper, zinc, magnesium, sodium, calcium, and the like, formingmetal sulfides which tend to remain suspended in the oils. The presentinvention is applicable to these treatments, particularly in so far asthey form suspensions of metal suldes which are not readily hydrolyzedand removed by washing with water.

The most common sweetening process is known as the doctor treatment.This treatment, and modifications thereof, involve the formation or useof metal suldes which tend to remain suspended in the sweetened oil tosome extent, thus requiring a water washing step and recovery of themetal suldes from the wash water.

The doctor treatment consists in agitating a sour distillate (onecontaining mercaptans) with a controlled amount of sulfur and analkaline sodium plumbite solution. The reaction results in theconversion of mercaptans to less objectionable organic disulfides andthe formation of lead sulfide. Most of the lead sulfide formed isseparated by settling from the treated oil but some remains suspended orentrained in the sweetened oil., Accordingly, this oil is washed withwater to remove the remaining suspended lead sulde.

With the procedure of washing hitherto used. it has been impractical toremove satisfactorily the suspended lead sulfide from the sweetened oilto the extent desired due to limitations of time, apparatus, and theamount of wash Water; and as a result, substantial amounts of leadsulfide left in the oil annoyingly have settled out in storage tanks.YUse of wash water in extra large vquantities makes recovery of the metalsulfide more diflicult, because a portion of the metal sulfide tends toremain in the water phase. and results in a greater loss of lead,excessive hydrocarbon product, and troubles from pollution of streams orrivers by the waste Water. Consequently, it is very important to improvethe water Washing procedure so as to obtain a more rapid separation ofthe lead sulfide with a restricted amount of water and apparatus.

In accordance With the present invention, certain organic substances,particularly high molecular weight proteins, which characteristicallyform mucilaginous colloids with water, are used effectively to expeditethe separation of the metal sulfide, up to the last traces thereof, froma sweetened hydrocarbon oil in the washing step, and thereby leave aclear sweetened product.

For example, by admixing a small amount, e. g., about 0.25% by weight ofgelatin or casein with a certain amount of Wash water, the time forseparation of lead suliide from a sweetened naphtha was shortened toabout 1 minute and less, whereas by omitting thesel agents, from about25 to 50 times as much time was required for the separation.

The amount of thesehigh molecular Weight protein agents required formaking-a considerable increase in the separation rate is very small.being of the order of from about 0.05% to about 1% by weight of thewater, and more beneficially in the range of 0.1% to 0.5%; therefore,they are used in an extremely small proportion with respect to thehydrocarbon liquid treated, since only about 5% to about 30%Y by volumevof water is used on the basis of the hydrocarbon liquid subjected towashing. n

The agents found to `be useful in thema-nner described for-improving thewashing procedure vary to some extent in composition .and in certainproperties; hence, there is some variation in the convenience of theiremployment and in their relative effectiveness. v

Gelatin, which behaves very satisfactorily, is a typical high molecularweight protein. It swells in cold Water and dissolves on heating to forma viscous liquid, which on recooling, solidies to a gel. .Howeven dilutesolutions used in'this procedure are not particularly viscous. Forexample, using 10% by Volume vof washy water containing 0.25% by Weightof gelatin forvwashing a sweetened naphtha containing a small amount ofsus pended lead sulfide following sweetening and settling, the lasttraces of lead sulfide were removed by this washing in about 1 minute.

Casein was used also with satisfactory results. Casein is the mostimportant protein constituent of milk. lt resembles other proteins, butcontains a small amount of phosphorus. It isrinsoluble in water, buteiiective amounts of casein were dispersed satisfactorily in the washwater with the addition of a small amount of an alkali, e. g., sodiumhydroxide. Using 10% by volume of wash water containing 0.25% by weightof casein for washing a sweetened naphtha containing a small amount ofsuspended lead sulfide, following sweetening and settling, final tracesof the lead sulde were separated out by this washing in about 30seconds.

In addition to the typical high molecular weight proteins mentioned,which characteristically form with Water a mucilaginous mass or glue,there are a number of others having these characteristics which may beused, but which are ordinarily less available and more expensive.

The preferred types of agents for aiding separation of the suspendedmetal suliide in the washing step are those that are stable under thetreating conditions, are readily dispersed homogeneously or colloidallyin the wash water before or during its contact with the hydrocarbonliquid, and which leave the washed hydrocarbon liquid in a neutral andpuried condition.

For the purpose of illustration, a preferred embodiment of the inventionwill be described with reference to a doctor swcetening process.

In the drawing is shown a flow diagram for a continuous doctorsweetening plant in which the present process may be applied.

Referring to the drawing, a sour petroleum distillate to be sweetened ischarged by inlet line I into mixer 2, equipped internally with oricemixing plates 3. In this mixer, the sour oil distillate is intermixedand agitated with the doctor treating solution (alkaline sodiumplumbite) entering the mixer from line 4. Generally, the sour oilentering the mixer contains the desired amount of added free sulfur.

From the mixer 2, the reaction mixture is passed by line to the leadsulde settler 6, in which lead sulde settled to the bottom is withdrawntogether with spent treating agent by line 1 for regeneration andfurther use.

sweetened oil, from which most of the lead sulde has been settled, iswithdrawn from settler l5 by line I0 to the water washing tower IIequipped with Wash water inlet I2, pressure control outlet I 3, spentwash water drain I4, and finished oil product outlet I5.

The spent wash water is delivered by line I4 to a water settling tankI5, equipped with a bottom drain I6 for removal of water substantiallyfree of lead sulde which may be recycled to wash tower I I, anintermediate take-off line I'I for removal of water containing aconcentrated suspension of metal sulfide, and skimming line I8 forremoval of surface layer of oil substantially free of lead sulde.

The intermediate aqueous layer withdrawn by line I9 may becentrifugedfor further concentrating the metal sulde, which may be then subjectedto regeneration.

Although the agents employed in accordance with the present inventionare admixed preferably and most conveniently with the water before it issupplied to the wash tower II by inlet line I2, they may be injectedseparately at any suitable point to facilitate settling in tower 6 or tofurther facilitate concentration of the metal suliide in the watersettler I5.

The use of the settling agents herein described may be practiced invarious modifications of the doctor treatment. They may be used wheresweetening is conducted in a batch system. They may be employed inobtaining more rapid and (ill complete separation of suspended metalsulfide when lead sulde is used by itself as a sweetening agent or withsome other metal compound.

It is to be noted that the high molecular weight protein agents whichwere found satisfactorily effective are substantially insoluble in thehydrocarbon oils but have a certain amount of aflinity for water. Ingeneral, they are neutral and nonionic. Thus, the preferred agents,particularly of the gelatin type, are benecially used in obtaining aneutral finished distillate satisfactorily free of the agent and metalsalts.

In general, the washing treatment is carried out near atmosphericpressure ranging up to about 30 lbs/sq. in. gauge and at temperaturesvarying from about 30 F. to 120 F.

The protein agents described have been used to obtain the rapidlycompleted separation of metal sulde from the sweetened distillate withabout half the amount of wash water ordinarily used.

A further advantage with the separation agents of the protein type isthat they may be used eiectively to concentrate the metal sulfide in arelatively small aqueous layer between a substantially sulde-free upperoil layer and lower` body of water` in a water settler, so`that recoveryof the concentrated metal sulde is facilitated, the used wash Water inthe bottom layer is in suitable condition for recycling, and a goodrecovery of the hydrocarbon product from the spent wash Water isobtained.

It is not intended that the invention be limited to the specic exampleswhich have been given for the purpose of this illustration, but it isintended that all modifications coming within the spirit of theinvention be included in the scope thereof as defined in the appendedclaims.

We claim:

1. In a process of sweetening hydrocarbon distillate oils containingmercaptans involving the dispersion of metal suldes in the sweeteneddistillate product, the step of separating the last traces of said metalsuldes from the oils which comprises washing the sweetened oil with asmall amount of a high molecular weight protein having ailinity forWater, mucilaginous colloid forming characteristics, andoil-insolubility.

2. In a process of sweetening a sour petroleum distillate by a doctorsolution of alkaline sodium plumbite, the step of removing the lasttraces of lead sulfide from a sweetened oil which comprises washing thesweetened oil with Water containing a small amount of gelatin dispersedtherein.

3. In a process of sweetening a sour petroleum distillate by a doctorsolution of alkaline sodium plumbite, the step of removing final tracesof lead suliide'from the sweetened oil which comprises washing thesweetened oil with Water containing a small amount of casein dispersedtherein.y

4. In a process of sweetening a petroleum distillate containingmercaptans with a compound of a metal which forms a suspension of metalsulde difficult to remove completely from thedistillate by Waterwashing, the improvement which comprises incorporating into Water usedto lwash out last traces of the suspended metal sulfide from thesweetened distillate about 0.05% to 1% of a high molecular weightprotein, characterized by hydrocarbon-oil-insolubility and ability toform a gelatinous and mucilaginous mass 5 in Water.

5. The steps of Washing out and recovering linal traces of suspendedlead sulde from a doc tor sweetened petroleum distillate, whichcornprises washing said sweetened distillate with from about 5% to 30%by volume of water containing about 0.05% to about 1% by weight of ahigh molecular weight protein of a type effective to concentrate themetal sulfide in a relatively small aqueous layer between asubstantially sulfide-free upper oil layer and a lower body of Water,separating spent wash water from the distillate, said spent wash watercontaining lead sulde and entrained hydrocarbons, settling said spentwash water in a settling zone, wherein three layers are formedcomprising a bottom layer of water substantially free of lead sulde andsuitable for recycling as water Wash, an intermediate aqueous layercontaining suspended lead sulfide, and a top layer of hydrocarbonssubstantially free of lead sulfide, and separately recovering materialsfrom each of said layers.

6. In a process of sweetening a naphtha distillate containing mercaptanswhereby a small amount of lead sulde remains suspended in the sweeteneddistillate, the improvement of removing final traces of the suspendedlead sulfide by washing the sweetened distillate with water containingabout 0.1% to 0.5% by weight of gelatin.

'7. In a process of sweetening a naphtha distillate containingmercaptan's whereby a small amount of lead sulde remains suspended inthe sweetened distillate, the improvement of removing final traces ofthe suspended lead sulfide by washing the sweetened distillate withwater containing about 0.1% to 0.5% by weight of casein and a smallamount of an alkali.

8. In a process of washing a sweetened naphtha distillate containing asmall amount of suspended lead sulde to remove nal traces thereof fromthe distillate, the improvement which comprises washing said distillatewith about 10% by volume of Water containing about 0.25% by weight ofgelatin and separating from said distillate the wash water containinglast traces of lead sulfide removed in a period of about 1 minute.

9. In a process of sweetening hydrocarbon distillate oils containingmercaptans involving the dispersion of metal suldes in the sweeteneddistillate product, the step of separating the last traces of said metalsulfides from the oils which comprises washing the sweetened oil with asmall amount of a protein selected from the group comprising gelatin andcasein.

MINORl C. K. JONES. RICHARD C. BRANDON.

